Read This Before All Your Brain Cells Are Gone (And They’re Going Fast!)

Written by Jason Dias

If you hope your brain cells die before they get old you won’t be disappointed. You once had 100 billion. By 40, you have just 40 billion. Read this quick, before they’re all gone …

aNewDomain — Kids have tons of potential.

That’s because they have tons of neurons, the brain cells primarily implicated in thought.  By the age of five or so, a human has some hundred billion of these little things.  Then something seemingly strange starts to happen: developmental pruning.


By the time we’re forty or so, we have only forty billion neurons left (give or take).  The rest have died, been converted mostly to waste, eliminated from the body.

So why does the brain continue to grow and intelligence continue to develop?

It turns out we don’t really need 100,000,000,000 neurons at all.  What we need are synapses.

Synapses are the connections between neurons.  By the time your brain is done developing into an adult configuration, it has between a hundred trillion and a quadrillion synapses.  Thought seems to be the firing of networks of neurons that represent our experiences: mentation, emotion, language, movement, sensory experiences.  Each neuron can connect to up to 10,000 other neurons to make these networks.

If your brain retained all hundred billion neurons, the number of synapses would be simply unsustainable.  Our brains already use 20-25% of all the calories we burn in a day.  So why have so many neurons and shed more than half?


What humans are really good at is fitting into whatever environment they are born into.  At adapting to the conditions of their lives.

We can learn any language, any customs, any forms of dance or sport, any technical skills.  When you were young, you had amazing potential, to be almost anything, to be nearly anyone.  Your experiences selected which neurons would be co-opted into networks to represent what was needed in your brain to make you a success.  It also selected which neurons, by not being networked in, would be allowed to die away to make room for synapses.

It’s like having a giant block of marble.  You cut away what is not needed to reveal some form within, to make it whatever is needed.

So at age five, learning was easy.  Languages, relationships, skills, customs, traditions.  At forty, some kinds of learning are more difficult.  Most of us struggle to learn new languages, for example. We just don’t have the extra neurons laying around our Broca’s and Wernicke’s areas to co-opt into networks to represent things in new words.  But we can adapt our learning style to compensate for other kinds of learning.

Young children accommodate.  That is, they build whole new schemas for new information or experiences.  They create new neural networks to accomplish this.  But adults with experience can instead assimilate new information.  This means to just expand existing networks.

For example, we often describe the brain as being like a computer system.  This is because adult learners already understand some things about computer systems.  Using metaphors such as this allows the adult to hand new information on the old information.  If you can understand computers, you can understand brains — with a little work.

And this is why sitting and listening are two things not good for adult learners.  We need more action and activity, the chance to convert things from dry readings and lectures into something that relates to our prior experiences.

Anyway, as we age, our potential fades.  That sounds sad, except the potential is replaced with actualization.  In other words, out of the near-infinity of potentials, some of them are made real in the world.

They say as you age you become ever more yourself.  The potentials I have actualized include a tendency to eat too much and move around too little, deep affection for words, and some effortful empathy.  Of course we continue to develop as we age, all the way until our final breaths.  But if I keep becoming this self, ever more refined, I think I’m going to need Richard Simmons to rescue me from my house.  I’ll cry with him, if he can pry the book out of my hands first.

For aNewDomain, I’m Jason Dias.

Cover image: GerryShaw [GFDL or CC BY-SA 3.0], via Wikimedia Commons
Image inline: GerryShaw (Own work) [CC BY-SA 4.0], via Wikimedia Commons